Hello again 
,
I think the problem is not the speaker (??). I tested other 4 different speakers with my sound card and a simple jig. Each test shows the same impedance ripple at high frequency... what did i do wrong? is this my faults or my system? I listed my test system below...
speaker work shop setup:
- sample rate : 48k (i obtain this from rrma)
- sample size : 256k
- I/O volume : 100
- mls signal repeat count : 10
- i've done all calibrations.
- impedance jig definition : 10.42 ohms
- series resistance : -136.4 mohms
- sound card input resistance : 15.47Kohms
- sound card inpu capacitance : 2.481 nF
Here is a simple jig i use:
Here are the channel difference calibration (show only the left channel which almost identical to the right) :
two speaker impedance tests are below:
please tell me where my problem is????
Thank you..
,I think the problem is not the speaker (??). I tested other 4 different speakers with my sound card and a simple jig. Each test shows the same impedance ripple at high frequency... what did i do wrong? is this my faults or my system? I listed my test system below...
speaker work shop setup:
- sample rate : 48k (i obtain this from rrma)
- sample size : 256k
- I/O volume : 100
- mls signal repeat count : 10
- i've done all calibrations.
- impedance jig definition : 10.42 ohms
- series resistance : -136.4 mohms
- sound card input resistance : 15.47Kohms
- sound card inpu capacitance : 2.481 nF
Here is a simple jig i use:
An externally hosted image should be here but it was not working when we last tested it.
Here are the channel difference calibration (show only the left channel which almost identical to the right) :
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
two speaker impedance tests are below:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
please tell me where my problem is????
Thank you..
Hi Kanan
Sorry for this late reply, but I was just now reading through this thread when I came upon this response. The first thing I always think of when deciding to design a low-budget pair of speakers is to use piezo tweeters. When properly crossed over these can sound much better than most budget tweeters (and some can even scare some of the big boys). There has been a lot written on them, but I have reproduced the post by Jon Risch (found at http://www.audioasylum.com/forums/pi/messages/556.html):
How to crossover a piezo:
Add a resistor in parallel, and the driver can be made to look like a current driven device to any outside components, such as a crossover cap. However, to keep costs and power dissipation down, 8 ohms is way too small of a value. The impedance of most piezo's is still quite high at 20KHz, so use a 22 ohm resistor, this makes any series crossover cap smaller and less expensive, and the resistor dissipates less energy. Use of an 8 ohm parallel resistor will also tend to lose you a little bit of output level.
For most piezos, use of a 22 ohm resistor, and a 4-4.7 uF cap will allow the response to be identical to what it was in stock form, but rolls off the lows at 6 dB/oct below 1 kHz or so. This actually increases the power handling of the piezo, as it is voltage limited. Exceed the voltage used to pole (polarize the piezo element during manufacture) the unit, and it will loose sensitivity, and eventually burn out. Most pro grade piezos will handle 35 volt transients, and 28 volts continuous, which are 150 watts and 100 watts into 8 ohms respectively.
Add in the cap and 22 ohm resistor, and the power handling could effectively be quadrupled, as the LF voltages are not imposed upon the unit, just the HF voltages.
Piezo's crossed over in this manner don't sound as harsh and spitty, and tend to be quite a bit more reliable. Many of the piezo units have a mild peak just before they roll off in the LF, so making the series cap a little smaller can actualy flatten response, and provide even more protection and smoother sound. For the smaller piezo units that cut off at 4-5 kHz, a series cap of 1.5 uF will do the trick, larger units that go down to 3 kHz can use a 2.2 uF, and the large compression driver units meant to be mounted on a horn need about 5 uF, as they do not peak, and any higher would lose the sloping LF output even more.
Attenuation, HF roll-off AND the crossing over can all be done at the same time. To attenuate, place a cap in between the piezo and the 22 ohm resistor that is shunting across the unit, then if HF roll-off is desired, use a series resistor in this location too. Then the series crossover cap should be in front of the 22 ohm shunt.
Looking from the amp, first the series crossover cap, say 4 uF, then the 22 ohm shunt from hot to ground, then a series cap of about 0.15 uF for 6 dB attenuation, and then a series resistor of about 30-50 ohms to tame the very top end, then the piezo itself.
I hope this helps, and I am sure if you use one of these that your speakers will sound a lot better than with the current tweeters that you have.
Enjoy,
Deon
Sorry for this late reply, but I was just now reading through this thread when I came upon this response. The first thing I always think of when deciding to design a low-budget pair of speakers is to use piezo tweeters. When properly crossed over these can sound much better than most budget tweeters (and some can even scare some of the big boys). There has been a lot written on them, but I have reproduced the post by Jon Risch (found at http://www.audioasylum.com/forums/pi/messages/556.html):
How to crossover a piezo:
Add a resistor in parallel, and the driver can be made to look like a current driven device to any outside components, such as a crossover cap. However, to keep costs and power dissipation down, 8 ohms is way too small of a value. The impedance of most piezo's is still quite high at 20KHz, so use a 22 ohm resistor, this makes any series crossover cap smaller and less expensive, and the resistor dissipates less energy. Use of an 8 ohm parallel resistor will also tend to lose you a little bit of output level.
For most piezos, use of a 22 ohm resistor, and a 4-4.7 uF cap will allow the response to be identical to what it was in stock form, but rolls off the lows at 6 dB/oct below 1 kHz or so. This actually increases the power handling of the piezo, as it is voltage limited. Exceed the voltage used to pole (polarize the piezo element during manufacture) the unit, and it will loose sensitivity, and eventually burn out. Most pro grade piezos will handle 35 volt transients, and 28 volts continuous, which are 150 watts and 100 watts into 8 ohms respectively.
Add in the cap and 22 ohm resistor, and the power handling could effectively be quadrupled, as the LF voltages are not imposed upon the unit, just the HF voltages.
Piezo's crossed over in this manner don't sound as harsh and spitty, and tend to be quite a bit more reliable. Many of the piezo units have a mild peak just before they roll off in the LF, so making the series cap a little smaller can actualy flatten response, and provide even more protection and smoother sound. For the smaller piezo units that cut off at 4-5 kHz, a series cap of 1.5 uF will do the trick, larger units that go down to 3 kHz can use a 2.2 uF, and the large compression driver units meant to be mounted on a horn need about 5 uF, as they do not peak, and any higher would lose the sloping LF output even more.
Attenuation, HF roll-off AND the crossing over can all be done at the same time. To attenuate, place a cap in between the piezo and the 22 ohm resistor that is shunting across the unit, then if HF roll-off is desired, use a series resistor in this location too. Then the series crossover cap should be in front of the 22 ohm shunt.
Looking from the amp, first the series crossover cap, say 4 uF, then the 22 ohm shunt from hot to ground, then a series cap of about 0.15 uF for 6 dB attenuation, and then a series resistor of about 30-50 ohms to tame the very top end, then the piezo itself.
I hope this helps, and I am sure if you use one of these that your speakers will sound a lot better than with the current tweeters that you have.
Enjoy,
Deon
Looking at those graphs you've produced leads me to believe that there's an amount of oscillation being introduced by your soundcard.
Its tricky to diagnose but I'd start with trying a different soundcard, checking the cable or redoing the entire Speaker Workshop setup again. Maybe you could also try other testing software such as AudioTester(Free trial version available).
Its tricky to diagnose but I'd start with trying a different soundcard, checking the cable or redoing the entire Speaker Workshop setup again. Maybe you could also try other testing software such as AudioTester(Free trial version available).
Hello everyone,
Bob, thank you for the guide, it's very helpful. Now i think i figured out the problem....calibration...
i'm working on calibration following Claudio Negro's guide. his guide is very easy to understand. I have done some calibrations and the output graphs look much better than ever. no more impedance ripple.
DeonC,
Thank you for your suggestion. I got this idea of using a piezo(a cheap one,~$0.25) as a tweeter yesterday. But i think i'll use it as a calibrator for my eletret capsule. my big problem is i live in a small province in thailand, it's very difficult to find a good speaker and impossible for a good piezo. Actually i can get a good speaker from bangkok but the price will break my philosophy. Another reason, i've already bought a pair of tweeter and i don't wanna throw it away . Anyway thank you for your suggestion, i'll keep it in mind for the next project 
.
ShinObiwan,
I think i know the problem. the pictures below show the new sound card calibration result...
Bob, thank you for the guide, it's very helpful. Now i think i figured out the problem....calibration...
i'm working on calibration following Claudio Negro's guide. his guide is very easy to understand. I have done some calibrations and the output graphs look much better than ever. no more impedance ripple.
DeonC,
Thank you for your suggestion. I got this idea of using a piezo(a cheap one,~$0.25) as a tweeter yesterday. But i think i'll use it as a calibrator for my eletret capsule. my big problem is i live in a small province in thailand, it's very difficult to find a good speaker and impossible for a good piezo. Actually i can get a good speaker from bangkok but the price will break my philosophy.
Another reason, i've already bought a pair of tweeter and i don't wanna throw it away . Anyway thank you for your suggestion, i'll keep it in mind for the next project .ShinObiwan,
I think i know the problem. the pictures below show the new sound card calibration result...
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Here is what i'm wating for.....
I've never seen any other tweeter. What do you think about it?
finally...
An externally hosted image should be here but it was not working when we last tested it.
I've never seen any other tweeter. What do you think about it?
finally...
kanan said:Here is what i'm wating for.....
An externally hosted image should be here but it was not working when we last tested it.
I've never seen any other tweeter. What do you think about it?
finally...
That curve looks a little 'rough'.
I'd almost certainly cross it over 4Khz if that was me, the sharp phase changes don't look good.
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